Production of ketene



formed during the reaction.

United PRODUCTION OF KETENE No Drawing. Application June 15, 1953 SerialNo. 361,864

6 Claims. (Cl. 260-5855) ,This invention relates to the production ofketene and relates more particularly to an improved process for theproduction of ketene by the catalytic pyrolysis of acetic acid.

An important object of this invention is to provide an improved processfor the production of ketene by the catalytic pyrolysis of acetic acidwhich will produce a maximum yield of the desired product with a minimumof decomposition.

A further object of this invention is to provide a process for theproduction of ketene by the catalytic pyrolysis of acetic acid which maybe carried out under such conditions of operation as to permit the useof relatively simple equipment.

Other objects of this invention will be apparent from the followingdetailed description and claims.

Ketene, a valuable intermediate for the synthesis of organic compounds,has long been produced by the vapor phase pyrolysis of acetic acid atsubatmospheric pressures. Such a process, in commercial application,imposes problems in the design and maintenance of equipment suitable foroperation at subatmospheric pressures and capable of handling high gasvelocities at high temperatures, followed by rapid cooling andseparation of gas and liquid streams in order to separate the ketenefrom the reaction mixture. It is also difiicult in such a system toobtain ketene free of acetic acid and water vapor because of theincreased partial pressure of these latter substances at subatmosphericpressures. Furthermore, in order to utilize the ketene obtained in thismanner, it is generally necessary to compress the ketene to atmosphericpressure or above, during which compression there is the danger of thepolymerization of the ketene to undesirable by-products.

According to the present invention, it has been found that ketene may beobtained in high yields by the vapor phase catalytic pyrolysis of aceticacid at pressures ranging from atmospheric to about 20 pounds per squareinch if the conditions during the pyrolysis are controlled closely. Incarrying out the pyrolysis, acetic acid is vaporized and is introducedinto a reactor, the nature of which will be set forth below, which ismaintained at a temperature of between about 625 and 750 C. and ata-pressure of between atmospheric and about 20 pounds per square inchgauge. There is also introduced into the reactor a suitable pyrolysiscatalyst such as a phosphate. The vapors are caused to flow through thereactor at such a rate that they remain therein for between about 0.01and 5.0 seconds, but preferably between 0.5 and 3.0 seconds. For a givenyield, temperature is aninverse function of contact time. There is thenintroduced into the reaction mixture a substance, such as ammonia, whichwill neutralize the catalyst and retard recombination of the ketene withreacted acetic acid and also with the water The exit gases are thenrapidly cooled and the ketene, which remains in gaseous form, isseparated from the liquid products rapidly as, for example, in a cycloneseparator. The ketene may, if

aren't O "ice desired, be further cooled to 0 C., or less, by means ofrefrigerated condensers or the like to free the ketene of all but tracequantities of water and acetic acid.

The material from which the reactor is constructed is critical sincemany materials such as nickel, chromium and iron will cause the keteneto be converted to other substances if they are brought into contactwith the hot reaction mixture or will fail to withstand the highreaction temperature. It has been found that steels containing betweenabout 3 and 4% of molybdenum and between about l7 and 20% chromium and 8to 12% nickel as major alloying metals will not cause the conversion ofthe ketene into other, less desirable substances. Suitable steels ofthis type are, for example, types 316 or 317 stainless steel. Thereactors should be designed and constructed to have good heat transferproperties with small temperature differential between wall. and gas,thereby minimizing degradation of the ketene at the wall.

To obtain a maximum yield of ketene, it is also desirable that thecondensers for cooling the hot reaction gases and separating the ketenefrom the liquid materials in said gases should have a high surface tovolume ratio and a high heat transfer coefiicient. In general, goodresults have beenobtained by employing condensers in which there is atleast about and preferably from about 140 to square feet of surface ofeach cubic foot of volume.

In carrying out the foregoing process, there is obtained, in addition tothe desired ketene, a certain proportion of acetic anhydride, presumablyby reaction of the ketene with acetic acid. This lowers the netefiiciency of the process, as calculated on the production of ketene.Therefore, according to another feature of the present invention, thereis added to the feed stock a certain proportion of acetic anhydride,preferably by recycling the acetic anhydride that is formed by thereaction. It is found that by having present in the feed stock a certainproportion of acetic anhydride, the conversion of acetic acid to aceticanhydride is substantially reduced. As a result, in a recycle system, asteady state will be reached in which no net change in the quantity ofacetic anhydride willoccur. Under these conditions, all the acetic acid,will, in eifect, be converted to ketene. A

After the ketene has been separated from the unreacted acetic acid, andthe acetic anhydride and water formed during the reaction by cooling,the condensed liquid is distilled with a suitable azeotroping agent suchas benzene or hexane to remove the water and the residue is recycled tothe reactor along with fresh acetic acid feed.

Pyrolysis catalysts other than triethyl phosphate that may be employedin carrying out the reaction include,

for example, diammonium phosphate, tri-cresyl phosphate or other estersof phosphoric acid. The pyrolysis catalyst may be added in amountsranging from about 0.2. to 0.5% by weight, based on the Weight of thefeed stock. Neutralizing materials other than ammonia that may be addedto the reaction mixture when it emerges from the reactor include, forexample, pyridine, aniline or suitable aliphatic amines. Theneutralizing agent should be added in amounts sufiicient to neutralizethe pyrolysis catalyst or, preferably, a slight excess. If desired, thecatalyst may comprise a salt of a volatile base such as ammoniumphosphate, dimethyl ammonium phosphate or pyridinium phosphate, in whichcase the neutralizing agent will be present in the reaction mixture asit emerges from the reactor.

The following examples are given to illustrate this invention further. II a i Example I Acetic acid feed stock containing 0.3% by weight of-trie'thyl phosphate is fed continuously at the rate-of454 31 partsperhourto aevaporizer and preheatedto. 5503, C... The vapors are thenintroduced into a reactor of type 317 stainless steel operating atatmospheric pressure and at a-tempera-ture of 680 CI The flow-rate issuch; as corn? pared'to the size of the reactor, that the vaporsremain Astream of'am from the liquid products in a cyclone separator. The keteneis then cooled further to remove traces of waterand acetic acidtherefrom. There'is obtained a-yieldg on an -hourly rate, of '1 19.5parts byweight offketene, 80

hydride. 'Injaddition, there are obtained :18 'parts by weightot ventgas .per hour, which gas comprisesdegradaz tion productsofketene andacetic acid- T he conversion ofacetic acid to moles of ketene -isolatedis 38% and the overall efliciency is 92.5%

Similar results have beenobt'ain'ed'with pressures up to aae s s aa incha e firampl ili;

A "mixture Jot I approximately 50% by weight of aceti acid and 50% byweight of acetic anhydride containing v 03% by weight of triethylphosphate is fed continuously ttire. rate .QfJ1 parts perhcur. tea.ra rie andp heatsito .50Qf"C-.;..The. vaporsare.then introd'u'cedfinto 1a..reactor .of il'pefilf? stainlesssteel.operating at .atinos phericpresente and at. a temperature 05690 C. The A flow; rate issuch,ascompared to the size-ofthe reactor,

partsby-weight of- 'accticiaci'd and 121 parts-of acetic an.

4. oLchromium. and between about. 8 and. 12%...otnickelw and maintainedat a pressure of up to about 20 pounds per square inch gauge, at atemperature of between about 625 and 750 C., and controlling the flow sothat the vapors remain in the reactor between about 0.01 and 5.0seconds.

2. In a proeess-for'the productioniof ketepe by vapor phase pyrolysis,the steps which comprise passing the vapors of acetic. .acid and 'apyrolysis catalyst 'throughjw' reactor cornp 'ising steel alloycontaining betweeni'abjont 3 and 4% of molybdenum, between about17.jand20-% of chromium and between about 8 and 12% of nickel, andmaintainedat a pressure-of between atmospheric and about 20 poundsper'squareinch gauge, at a temperature of between about625 andi750" C,,and controlling the How so that the vapors remain in the reactor betweenabout 0.01 and 5.0 seconds.

In a pruccs for: h pr u ti n fkflsns bv apcr, pha p lysist t ps sompr Pi he 'ai-i pors of acetic acid'and a pyrolysis catalyst through a re:actor comprising a steel alloycontaining betweenv about 3 and 4%. ofmolybdenum, between about 17 and 20%. of chromiumtand between about-8and12%..of.niclte1,.. nd ma nta n t p es u c o be e a m sphe can about20 pounds per square inch gauge, ata tempera-M6:

v ofzbetweeniabout- 625': and-750 C1,. controlling the-flow at-the ape srem in iathe r action :zon af r- 0 1. e

ndz: A- streamofeammcnia isini t d iintofthe hot g ses"as-theydeave-thereactor at the rate of 4.5 parts by-weight' of ammoniaper hour. The hot gases arethen'cooled rapidly to 100 C.'in a condenserhaving a cooling area 4134; pa ts yl ht of r et e, 9.6.8 p rts. by e hieQ tiQQaC dau 0- P b weight 95 flicfipdn? hydride. In addition, thereisobtained 9.3 parts by weight ot vent gas There is a net-conversionotteed toketene; of 33.4%, together with an apparent conversion ofacetic n cidicee o l-6% and n..- ppa s c nve ion-0 cetic .an ydr d to .kt ne .ot--19,%:.t- The, effici ncy i of 1'41 squareteetforeach cubicfoot of-volume and the ketene is separated from the liquid products in acyclone The ketene is then cooled further to remove 94%. The acetic acidand =aceticlanhydride. produced.

are recycled together with fresh teed and,"when.,equilib-.

rium is reached, no further additions of acetic anhydride arerequired-At this point,-the-feed containsapproximately %by weight of acetic acidand 40% by weight of acetic anhydride;

Similar results are obtained when the pressure ,iS-ill-Q creased to 16pounds persquare inch gauge.

Hits to be understood that the foregoing detailed def c ipt uissivecmyby y of l t n a d that.

many yariationsmay be made therein without departing from the spirit ofour invention.

Having; described our invention, what .we. d esire toflse cureby LettersPatent is:

. theeercse s o -tber edust eaenf:hte ehwanc thnough ai reactono f type3-1.7. 'stainlessi steel maintained:

phase pyrolysis, the steps which comprise passingithey vapors of aceticacid and a' pyrolysis catalyst through a e t compr t e a loy-c mmitt n bw n b u 3 ssdt fesnf ht seaanietr een abeutal] acne so' that fthe'vapor's remain in the reactor between about? 0:01 'andiOsecondswhereby' there is obtained a mixture ot hotgases containingketene', adding a neutralim'ng" agent? I for the pyrolysis catalyst tothe hot gases as they 'emerg'e from-therea'ctor, rapidly cooling thehot-g'ases'as -they emerge from the reactor in a condenser having at'least'about'i'1 4'0 square feet of surface, for each cubictoot'of volume andrecovering the 'ketene. v '4 n. l pro s r e r uc on. of te e "by por;Phase py o ys t e teps. ic mp e .pass sa i xture ofacetic acid, aceticanhydride and a pyrolysis 'cata lyst .througha reactor comprising asteel alloy containing between. about 3v and 4% .of molybdenum, betweenabolnjtp 17 and.20%.o f chromiumand between about} and 12%- 0t nickeland maintained at:a pressure of between atmosphericzand'ahout;20:p.ounds per square inch gauge-at a? temperaturerofbetweenxabout 625 and 750 .C.', and con-1 rtrollingtheflow. so.:that'the: vapors remainin the reactor. between. about- 0. 01 and 5 .0seconds wherebytliere' is obtained a: mixture of-hotgases containingketene.

5. ln a process'ior the production of ketene-by-vapor phase pyrolysis,thesteps which comprise passing a miir ture of acetic acid, aceticanhydride and ,a phosphate 'py--" rolysis catalyst"throughga reactorcomprising a steel a1 y ont inin b tw u'abcu 3 a d .nc yhd um,; betweenabout 1*Tan'd 20%jchromium; and'between, about 8 kt 1 I ma n ained at apressureott be tween atmosphericfand about 20' pounds per square inch Q,gauge, .at a temperature of between about 625 and750 C., controllingtheflow sothat the vapors remain inthe, reactor between about 0.01 and5.0 seconds thereby forming. amixture of hotgases containing ketencandtz phosphate,- iadding ammonia to I the. hot gases as they emerge,from'the reactor to neutralize the phosphate,-and rapidly cooling thehot gases as they emerge from the re actor in a condenser having hetweenahout 'and- 180" square feet of surface for each cubictoot of volume.

l 6. .In'aprocess'for the production of ketene' by'vapor; Phase h dro ys e steps h c m p s 's'a m xi i m'reot a et c. acid. ac uhydr t c hylphosph te at at o e ic-p ssing e d-a a emper tu e o -z cce tiaa tbefl hte sepsis: we i eac er' 0' asiztheyri tnerge'trom thereagtorstoineutrali,tt te.:phos.-.;=t

diam n addin ia mcr s-t t t? ass s phate, cooling the hot gases as theyemerge from the reactor to a temperature of 100 C., in a condenserhaving a cooling area of 141 square feet for each cubic foot of volume,separating ketene from the hot gases, and recycling acetic anhydridefrom the gases through the reactor with fresh acetic acid.

References Cited in the file of this patent UNITED STATES PATENTSHemminger Feb. 20, 1951

1. IN A PROCESS FOR THE PRODUCTION OF KETENE BY VAPOR PHASE PYROLYSIS,THE STEPS WHICH COMPRISES PASSING THE VAPORS OF ACETIC ACID AND APYROLYSIS CATALYST THROUGH A REACTOR COMPRISING STEEL ALLOY CONTAININGBETWEEN ABOUT 3 AND 4% OF MOLYVBDENUM, BETWEEN ABOUT 17 AND 20% OFCHROMIUM AND BETWEEN ABOUT 8 AND 12% OF NICKEL, AND MAINTAINED AT APRESSURE OF UP TO ABOUT 20 POUNDS PER SQUARE INCH GAUGE, AT ATEMPERATURE OF BETWEEN ABOUT 625 AND 750%C.M AND CONTROLLING THE FLOW SOTHAT THE VAPORS REMAIN IN THE REACTOR BETWEEN ABOUT 0.01 AND 5.0SECONDS.